Prestretching cellulose derivative yarns to increase tenacity



Patented May 29, 1951 'PRESTRETCHING CELLULOSE DERIVATIVE YARNS TO INCREASE TENAOITY Thomas Barnard Frearson and Edgar Alfred Goodall, Spondon, near Derby, England, assignors to Celanese Corporation of America, a

corporation of Delaware N Drawing. Application June 9, 1948, Serial No. 32,048. In Great Britain June 24, 1947 7 Claims. (01. s 132).

This invention relates to processes for increasing the tenacity of artificial yarns and filaments having a basis of a thermoplastic organic derivative of cellulose by stretching them under the influence of an aqueous softening agent beyond their elastic limit.

As is known from a number of U. S. Patents Nos. 2,142,716; 2,142,717; 2,142,721; and 2,142,722 the tenacity of cellulose acetate filaments, yarns and like materials (all hereinafter referred to as yarns), and of similar materials of other cellulose esters or of cellulose others, can be substantially increased by stretching the yarns in the presence of saturated or wet steam or hot water under pressure at temperatures above 100 C. With the higher stretches, it was found desirable to eliminate or reduce the tension exerted on the yarns at the inlet to the stretching chamber by the stream of steam or hot water escaping from the inlet orifice, and U. S. Patents Nos. 2,142,909; 2,142,910 and 2,142,912 describe a device comprising an end box through which the yarns or other materials pass before they enter the stretching chamber. This end box may contain an inert gas, such for example as compressed air, or may contain water at room temperature or at a temperature insufficiently high to produce any substantial softening of the yarns. The yarns may be fed through the device for example by pairs of nip rollers outside the end box, in the end box and beyond the stretching chamber, the relative speeds of the last two pairs of rollers being such as to impart the desired degree of stretch to the yarn as it passes through the stretching chamber. cation S. No. 472,460, filed January 15, 1943, now U. S. Patent No. 2,450,045 describes an injector device designed to feed the yarns into the stretching chamber and, in a preferred formof the injector, provides for the injection of water with the yarn, thus reducing the tension exerted on the yarns at the entrance to the stretching chamber without making use of an end box. The reduction of tension in th yarn at and before its entry into the stretching chamber, Whether by using an end box or an injector, has been found to give a substantially improved product, particularly when the yarns are stretched by about 5-20 times their original length or more. In practice, the yarn, before entering th stretching chamber, has been subjected to as light a tension as possible.

We have now found that it is of advantage, from the point of view both of ease of manipulation and of the quality of the stretched product, to subject the yarns before they enter the stretching chamber and in their normal, i. e. unsoftened, state to a pre-stretching operation, the degree of pre-stretch being not more than about 80% of their extensibility under the prevailing condi- U. S, Patent No. 2,279,479 and appli- 2 tions. (The term stretch is here applied to an extension of the yarn suificient to give'it a permanent elongation, that is to say' the amount of pro-stretch applied is more'than the normal elon gation of the yarn conforming with Hookes law.

The term extensibility is used to denote the greatest degree to which the unsoftened yarns can be stretched Without breaking; the extensibility depends to some extent on the conditions prevailing; for example a wet yarn has a some what higher extensibility than the same yarn when dry). on the yarn in the dry or wet state; in the former case the amount of the pre-stretch with ordinary commercial cellulose acetate yarns may be between 2 and 20% of their original length, and in the latter between 2 and 25%. The preferred amount of pre-stretch is of the order of 60-75% of the dry or wet extensibilit of the yarn as the case may be. the extensibility of the yarn under the conditions in which the pre-stretch takes place generally lead to difficulties in the further processing.

The pro-stretch may be carried out by feeding the yarn first through a pair of rollers outside the stretching apparatus and then through rollers.

located in an end box of the type described in U. S. Patents Nos. 2,142,909; 2,142,910 and 2,142,- 912 or first through two sets of rollers outside the stretching apparatus and then through an injector device into the stretching chamber, for instance as described in U. S. Patent No. 2,279,479

and application S. No. 472,460, filed January 15,-

1943 noW U. S. Patent No. 2,450,045. In both methods the two sets of rollers are driven, pref-- erably by positive gearing, at speeds which will impart the desired degree of pre-stretch. If the yarns are to be pro-stretched Wet, they may with advantage be thoroughly wetted before passing through the first pair of rollers, for example by the method described in U. S. Patents Nos. 2,279,-;

478 and 2,279,479; if desired, ho wever, they may be wetted while travelling between the two pairs; of rollers, e. g. by passing them through a trough or other suitable vessel containing water, which may beat room temperature'or ata higher tem' paratus described in the specifications referred,

to above. For instance a 225 denier yarn of cellulose acetate of viscosity about 60' (as hereinafter defined) may be thoroughly, wetted with This pro-stretch may be carried'out' Pro-stretches exceeding of water and then passed between two positively driven sets of rollers whereby it is pie-stretched by about 23% of its original length, and may then be fed into a stretching chamber by means of a device such as is described in U. S. Patent No. 2,279,479 and application S. No. 472,460, filed January 15, 1943, now U. S. Patent No. 2,450,045, and then stretched by about times its original length while in contact with wet steam at 39.5

The new process may be applied to cellulose acetate yarns of different viscosity characteristics, including yarns of cellulose acetate of moderate viscosity, e. g. -20, or of high viscosity, e. g. 40-80 or more. (These viscosities are determined by comparing the rate of flow of a 6% solution of the cellulose acetate in acetone at C. with that of glycerine taken as 100.) It is also applicable to yarns having a basis of another cellulose derivative, e. g. of another cellulose ester such as cellulose propionate, cellulose butyrate, cellulose acetate-propionate or cellulose acetate butyrate, or of a cellulose ether, for example an ethyl cellulose soluble in organic solvents. The invention is applicable both to yarns made up of continuous filaments and to yarns spun from staple fibre.

The application of a constant substantial degree of pre-stretch in accordance with the invention gives rise to a product having several advantages over that obtained without pre stretching. Thus there is an improvement in the uniformity, especially the denier-uniformity, of the stretched yarns, and the whole stretching operation becomes easier to perform, and does not call for so high a degree of skill and experience on the part of the operator. Further, the use of positive gearing, which becomes advantageous when a substantial degree of pre-stretch is to be applied but which is in general inconvenient or even impracticable in the older stretching processes, may also play a part in increasing the uniformity of the product.

The new process may be applied to yarns, either singly or in warp formation, of widely differing denier. It is moreover of value not only for treating bundles of yarns of fairly low or moderately high total denier, but also in the treatment of large bundles of yarns, particularly bundles having an initial total denier above about 100,000, e. g. 200,000, 300,000, or up to 500,000, which are subsequently to be converted into staple fibre by breaking or cutting and subsequent spinning. Such large bundles may conveniently be made up from a number of smaller bundles, and it is believed that the pre-stretching operation serves to render these smaller bundles more strictly parallel before the main stretch is applied. Whatever the reason, it is found that by giving these large bundles a degree of pre-stretch in accordance with the invention a more uniform and also a stronger product can be obtained than when no prestretch is given, and that it becomes possible to produce from the bundles a better staple fibre yarn.

Having described our invention, what we desire to secure by Letters Patent is:

1. A process for increasing the tenacity of yarns of an organic derivative of cellulose, selected from the group which consists of cellulose esters or organic acids and cellulose ethers, by stretching the yarns to more than'5 times their original length in the presence of a softening agent selected from the group which consists of water, wet steam and saturated steam, all at a temperature above 100 C., wherein immediately before they are so softened and stretched, the yarns are given a constant degree of pre-stretch between 2 and of their original length, and below of their extensibility immediately before the pro-stretch is effected.

2. A process for increasing the tenacity of yarns of a lower aliphatic acid ester of cellulose by stretching the yarns to more than 5 times their original length in the presence of a softening agent selected from the group which consists of Water, wet steam and saturated steam, all at a temperature above C., wherein immediately before they are so softened and stretched, the yarns are given a constant degree of prestretch between 2 and 25% of their original length, and below 80% of their extensibility im mediately before the pre-stretch is effected.

3. A process for increasing the tenacity of cellulose acetate yarns by stretching the yarns to more than 5 times their original length in the presence of a softening agent selected from the group which consists of water, wet steam fand saturated steam, all at a temperature above 100 C., wherein immediately before they are so softened and stretched, the yarns are given a constant degree of pre-stretch between 2 and 25% of their original length, and below 80% of their extensibility immediately before the prestretch is eifected.

4. A process for increasing the tenacity of cellulose acetate yarns by stretching the yarns to more than 5 times their original length in the presence of a softening agent selected from the group which consists of Water, wet steam and saturated steam, all at a temperature above 100 0., wherein immediately before they are so softened and stretched the yarns while in a dry condition are given a constant degree of prestretch between 2% and 20% of their original length;

5. A process for increasing the tenacity of cellulose acetate yarns by stretching the yarns to l more than 5 times their original length in the presence of a softening agent selected from the group which consists of water, wet steam and saturated steam, all at a temperature above 100 C., wherein immediately before they are so 1 softened and stretched the yarns are thoroughly wetted and given a constant degree of pre-stretch between 2% and 25% of their original length.

6. Process of claim 1, wherein large bundles of yarns of total denier between 100,000 and'500,000

. are subjected to the pres t retching and stretching operations.

7. Process of claim 3, wherein large bundles of yarns of total denier between 100,000 and 500,000 are subjected to the pre-stretching and stretching operations.

THOMAS BARNARD FREARSON. EDGAR ALFRED GOODALL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,709,470 Hall Apr. 16, 1929 2,137,235 Carothers Nov. 22, 1933 2,142,719 Dreyfus et al. Jan. 3, 1939 2,307,846 Miles Jan. 12, 1943 2,389,655 Wende Nov. 27, 1945 

1. A PROCESS FOR INCREASING THE TENACITY OF YARNS OF AN ORGANIC DERIVATIVE OF CELLULOSE, SELECTED FROM THE GROUP WHICH CONSISTS OF CELLULOSE ESTERS OR ORGANIC ACIDS AND CELLULOSE ETHERS, BY STRETCHING THE YARNS TO MORE THAN 5 TIMES THEIR ORIGINAL LENGHT IN THE PRESENCE OF A SOFTENING AGENT SELECTED FROM THE GROUP WHICH CONSISTS OF WATER, WET STEAM AND SATURATED STEAM, ALL AT A TEMPERATURE ABOVE 100* C., WHEREIN IMMEDIATELY BEFORE THERY ARE SO SOFTENED AND STRETCHED, THE YARNS ARE GIVEN A CONSTANT DEGREE OF PRE-STRETCH BETWEEN 2 AND 25% OF THEIR ORIGINAL LENGTH, AND BELOW 80% OF THEIR EXTENSIBILITY IMMEDIATELY BEFORE THE PRE-STRETCH IS EFFECTED. 